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Alarm Pheromone Knocks Off Russian Wheat Aphids

The Russian wheat aphid is a major pest of
winter wheat and barley in the United States and worldwide. First identified in
1986 in the United States, the green, 1/16-inch-long Diuaphis noxia had
cost U.S. growers $1 billion by 1993.

Last year, cumulative yield losses topped 106 million bushels and infestation
of small-grains crops totaled over 20 percent throughout the pest's North
American range16 states and 2 Canadian provinces.

Searching for ways to outwit the pest and keep it from spreading, John D.
Vandenberg, of the U.S. Plant, Soil, and Nutrition Laboratory in Ithaca, New
York, and colleagues Paresh A. Shah and John A. Pickett from the Institute for
Arable Crops Research in Harpenden, England, made some new discoveries.

The team found that the Russian wheat aphid may produce the alarm pheromone
(E)-ß-farnesene and showed that the pest responds to it.

Alarm pheromones are produced by some aphids in response to a disturbance.
Their effect is to stimulate movement by nearby aphidsa response that may
help the pests avoid predators.

"(E)-ß-farnesene is a common alarm pheromone among aphids,"
Vandenberg says. "They release it from their rear abdomen, where it is
secreted when they are attacked by arthropods. A forced behavior, such as
dropping off the host plant, may help aphids avoid enemies."

Vandenberg and colleagues studied the Russian wheat aphid's response to a
synthetic form of the green peach aphid's alarm pheromone.

Vandenberg also evaluated the pheromone's effectiveness in combinations with an
aphid-infecting fungus, Paecilomyces fumosoroseus, in hopes that alarmed
on-the-move aphids would be more likely to become infected.

In a series of lab tests, the researchers found that aphids responded to the
alarm pheromone by removing their feeding tubes, or stylets, from barley leaves
and crawling out of test areas. They left even more quickly when the pheromone
concentration increased.

But combinations of (E)-ß-farnesene and the aphid-infecting fungus did
not enhance aphid mortality.

Vandenberg says, "Further studies are needed to determine whether the pest
actively secretes alarm pheromones in response to natural disturbances. Studies
are also needed to explore the possible synergy between pheromone applications
and other control agents."By
Hank
Becker, Agricultural Research Service Information Staff.